Reproductive steroid hormones are thought to regulate target cells by interacting with nuclear chromatin to produce altered gene products which in turn may direct the synthesis of specific proteins. Progesterone has been difficult to study at the molecular level in mammalian systems. We therefore characterized the progesterone- sensitive chick oviduct and showed it to be a representative model of progesterone action. New insights into sex steroid function recently have been possible through advances in three areas: hormone receptors, chromatin structure and RNA synthesis. We plan to integrate these areas and to study specific RNA synthesis resulting from purified receptor-chromatin interactions. Our approach will be: 1. Characterization of interactions between purified receptor subunits and nuclear chromosomal constituents. 2. Isolation of the chromatin "acceptor proteins" which bind the steroid-receptor complexes as they enter the nucleus. 3. Development of a hormone-responsive RNA synthesis system in vitro. 4. Analysis of hormone-receptor interactions with chromatin proteins by quantitative and qualitative changes in patterns of RNA synthesis. This work should afford a much clearer picture of molecular events at the transcriptional level, resulting in an advance in our understanding of reproductive steroid hormone action.